In some drilling operations, a top drive is suspended in a rig and a casing engaging and drive assembly is positioned therebelow. These tools support the drill string and may rotationally and axially drive it. These tools also permit circulation of drilling fluid through the drill string. A drill string valve may be incorporated in these tools.
In one embodiment, a drill string valve is incorporated in the top drive below the quill and may support an actuator thereabout. The valve is sometime termed a mud saver valve and may include one or more valve mechanisms for controlling drilling fluid flow to the drill string. Drill string valves used in top drive drilling operations are generally remotely functioned by an actuator. During a drilling operation, the valve because of its position in the stem below the quill of the top drive, may be required to support the weight of the drill string and to deliver the drilling torque to the string. Due to the dimensional constraints of typical actuators and the presence of stem or other holes in the valve, the valve may have an inherent weakness. In some applications, the combined load conditions including bending, axial weight and torque load conditions under which the valve is required to operate have caused the valve to fail, for example about its valve stem openings.
Another valve body dimensional obstacle is the need to provide for stripping the valve into the hole or casing being drilled through.
Since the valve is positioned above the drill floor, it may be desirable or necessary to achieve a particular rating for the valve, for example, of API8C. However, due to the above-noted constraints, it has been difficult to achieve such a desired API rating.